Hardware and method for implementation of in situ acoustic thermograph inspections

ABSTRACT

A system and method include an acoustic thermography stack and a frame that the stack is slidably mounted to. The frame includes an end frame portion with a blade stop, and an air cylinder provides force to move the stack up and down a rail of the frame such that a turbine blade may be clamped between a cap of the stack and the blade stop. The clamped blade is excited using the stack, and an infrared camera is used to detect critical indications in the blade.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to a system and method for performingthermograph inspection of turbine blades and, more particularly, to asystem and method for performing acoustic thermograph inspection ofturbine blades without removing the blades from the turbine so as toeliminate the need for costly blade removal to perform the inspection.

Discussion of the Related Art

The world's energy needs continue to rise which provides a demand forreliable, affordable, efficient and environmentally-compatible powergeneration. A turbine engine is one known machine that providesefficient power, and often has application for an electric generator ina power plant, or engines in an aircraft or a ship. A typical gasturbine engine includes a compressor section, a combustion section and aturbine section. The compressor section provides a compressed air flowto the combustion section where the air is mixed with a fuel, such asnatural gas, and ignited to create a hot working gas. The working gasexpands through the turbine section and is directed across rows ofblades therein by associated vanes. As the working gas passes throughthe turbine section, it causes the blades to rotate, which in turncauses a shaft to rotate, thereby providing mechanical work.

Maintaining the structural integrity of the blades in a turbine isimportant for proper operation of the turbine. Thus, it is veryimportant to periodically check the blades for signs of deterioration,such as cracks and defects. One known technique for testing for materialdefects in the blades includes treating the blades with a dye penetrantso that the dye enters any crack or defect that may be present. Theblades are then cleaned, and the structure is treated with a powder thatcauses the dye remaining in the cracks to wick into the powder. Anultraviolet (UV) light source is used to inspect the material to observelocations on the component that fluoresces as a result of the dye. Thistechnique is disadvantageous, however, because it is inspector intensiveand dependent and requires the person to be skilled. Additionally, thedye does not typically penetrate tightly closed cracks or cracks thatare not on the surface.

A second known technique for inspecting a component for defects employsan electromagnetic coil to induce eddy currents in the blade. The coilis moved around on the blade, and the eddy current pattern changes at acrack or other defect. When the eddy current pattern changes a compleximpedance in the coil changes, which can be observed on an oscilloscope.This technique has the drawback that it is also very operator intensive,slow and tedious.

A third known technique employs thermal imaging of the component toidentify the defects. Typically, a heat source, such as a flash lamp ora heat gun, is used to direct a planar pulse of heat to the surface ofthe component. The material of the component absorbs the heat, and emitsreflections in the infrared wavelengths. Certain types of defects willcause the surface temperature to cool at a different rate over thedefects than for the surrounding areas. A thermal or infrared imagingcamera is used to image the component and detect the resulting surfacetemperature variation. Although this technique has been successful fordetecting disbands and corrosion, it is ordinarily not successful atdetecting vertical cracks in the material, i.e., those cracks that areperpendicular to the surface. This is because a fatigue crack looks likea knife edge to the planar heat pulse, and therefore no, or minimal,reflections occur from the crack, making the cracks difficult orimpossible to see in the thermal image.

Thermal imaging for detecting defects in a material that is capable ofdetecting small cracks as well as tightly closed cracks is described inU.S. Pat. No. 6,399,948 issued to Thomas et al. on Jun. 4, 2002.However, this technique requires the material that is being inspected tobe placed in a thermal imaging system. Thus, if the material to beinspected includes turbine blades, the blades must be removed from theturbine to be inspected. Removal of turbine blades is costly,time-consuming and labor intensive. Thus, there is a need in the art fora system and method that allows for thermal imaging of turbine bladeswithout removing the blades from the turbine.

SUMMARY OF THE INVENTION

This disclosure describes a system and method for performing acousticthermography inspection of turbine blades. The system and method includean acoustic thermography stack and a frame that the stack is slidablymounted to. The frame includes an end frame portion with a blade stop,and an air cylinder provides force to move the stack up and down a railof the frame such that a turbine blade may be clamped between a cap ofthe stack and the blade stop. The clamped blade is excited using thestack, and an infrared camera is used to detect critical indications inthe blade.

Additional features of the present invention will become apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a gas turbine engine;

FIG. 2 is an illustration of a known turbine blade separated from a gasturbine engine;

FIG. 3 is an illustration of a cross-sectional view along line 3-3 ofthe blade shown in FIG. 2;

FIG. 4 is an illustration of an embodiment of a system for performingacoustic thermography of turbine blades that are part of an assembledsteam turbine;

FIG. 5 is an illustration of the system for performing acousticthermography where the system is being used inside of an assembled steamturbine;

FIG. 6 is an illustration of an infrared camera that is being used withthe system according to one embodiment; and

FIG. 7 is an illustration of the infrared camera being used with thesystem according to another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the invention directed toa system and method for performing in situ acoustic thermographinspection is merely exemplary in nature, and is in no way intended tolimit the invention or its applications or uses. For example, while insitu thermograph inspection of turbine blades in a steam turbine aredescribed herein, other types of in situ acoustic thermograph inspectionmay be used according to the system and method of the present invention.

FIG. 1 is a cut-away, isometric view of a gas turbine engine 10including a compressor section 12, a combustion section 14 and a turbinesection 16 all enclosed within an outer housing 30, where operation ofthe engine 10 causes a central shaft or rotor 18 to rotate, thuscreating mechanical work. The engine 10 is illustrated and described byway of a non-limiting example to give context to the invention discussedbelow. Those skilled in the art will appreciate that other gas turbineengine designs will also benefit from the invention. Rotation of therotor 18 draws air into the compressor section 12 where it is directedby vanes 22 and compressed by rotating blades 20 to be delivered to thecombustion section 14 where the compressed air is mixed with a fuel,such as natural gas, and where the fuel/air mixture is ignited to createa hot working gas. More specifically, the combustion section 14 includesa number of circumferentially disposed combustors 26 each receiving thefuel that is injected into the combustor 26 by an injector (not shown)and mixed with the compressed air to be ignited by an igniter 24 tocreate the working gas, which is directed by a transition 28 into theturbine section 16. The working gas is directed by circumferentiallydisposed stationary vanes (not shown) in the turbine section 16 to flowacross circumferentially disposed rotatable turbine blades 34, whichcauses the turbine blades 34 to rotate, thus rotating the rotor 18. Oncethe working gas passes through the turbine section 16 it is output fromthe engine 10 as an exhaust gas through an output nozzle 36.

Each group of the circumferentially disposed stationary vanes defines arow of the vanes and each group of the circumferentially disposed blades34 defines a row 38 of the blades 34. In this non-limiting embodiment,the turbine section 16 includes four rows 38 of the rotating blades 34and four rows of the stationary vanes in an alternating sequence. Inother gas turbine engine designs, the turbine section 16 may includemore or less rows of the turbine blades 34. It is noted that the mostforward row of the turbine blades 34, referred to as the row 1 blades,and the vanes, referred to as the row 1 vanes, receive the highesttemperature of the working gas, where the temperature of the working gasdecreases as it flows through the turbine section 16.

FIG. 2 is a cross-sectional view of a known airfoil or blade 40 that isintended to represent a row 1 blade, but can be a general representationof any of the blades 34 in the rows in the gas turbine engine 10, wherethe blade 40 includes cooling airflow channels discussed in detailbelow. FIG. 3 is a cross-sectional view of the blade 40 along line 3-3in FIG. 2. The blade 40 includes an attachment portion 42 that isconfigured to allow the blade 40 to be securely mounted to the rotor 18in a manner well understood by those skilled in the art. A bladeplatform 44 is provided at a distal end of the attachment portion 42 anddefines the beginning of a tapered airfoil portion 46 of the blade 40.The airfoil portion 46 includes a pressure side (P/S) 86 and a suctionside (S/S) 84 defined by the pressure present on the airfoil portion 46as it rotates. Further, the airfoil portion 46 also includes a leadingedge 80 and a trailing edge 82.

The airfoil portion 46 includes an outer housing 48 and a number ofinternal ribs 50, 52, 54, 56, 58 60 and 62, typically configured as asingle piece insert and being made of ceramic, that define a series offlow channels. The flow channels include a shower head flow channel 64between the outer housing 48 and the rib 50, a flow channel 66 betweenthe rib 50 and the rib 52, a flow channel 68 between the rib 52 and therib 54, a flow channel 70 between the rib 54 and the rib 56, a flowchannel 72 between the rib 56 and the rib 58, an impingement flowchannel 74 between the rib 58 and the rib 60, an impingement flowchannel 76 between the rib 60 and the rib 62, and an impingement flowchannel 78 between the rib 62 and the outer housing 48. The flowchannels 68, 70 and 72 combine to make up a serpentine flow channel. Airflows into the blade 40 through an input opening 90 in the attachmentportion 42, enters the channel 66 and flows towards an end portion 92 ofthe housing 48, where some of the airflow exits the flow channel 66through orifices 94. Some of that air flows through orifices 96 in therib 50 into the shower head channel 64 and out of the airfoil portion 46through a series of orifices 100 that are angled upward towards the endportion 92. Airflow also enters the blade 40 through an opening 102 inthe attachment portion 42 and flows into the channel 68 where some ofthe airflow flows out orifices 104. Most of the airflow flows into thechannel 70 to flow back down the airfoil 46 and into a chamber 106 inthe attachment portion 42 that has an opening covered by a cover plate108. The air then flows back up the blade 40 through the channel 72 andthrough orifices 110 in the housing 48.

The rib 58 includes a series of orifices 120 that allow the air to flowinto the channel 60 between the ribs 58 and 60, the rib 60 includes aseries of orifices 122 that allow the air to flow into the channel 62between the ribs 60 and 62, and the rib 62 includes a series of orifices124 that allow the air to flow into a channel 94 between the rib 58 andthe outer housing 48. A series of orifices 130 in the outer housing 48allows the air to flow out of the blade 40. As is apparent, the orifices120, 122 and 124 in the ribs 58, 60 and 62 are staggered relative toeach other so that the air does not flow directly from one channelacross the next channel into the following channel. This causes the airflowing through one of the orifices to strike a section of the rib inthe next channel also creating turbulence that increases the coolingeffect. Particularly, this airflow effect creates vortexes inside of thechannels 74, 76 and 78 that also provide turbulence for effectivecooling.

It is known in the art to provide a configuration of turbulators or tripstrips mounted to the inner walls of the flow channel portions 66, 68,70 and 72, represented generally as reference number 132 in FIG. 2. Atrip strip for this purpose is typically a metal strip formed to aninside surface of the outer housing 48 of the blade 40 in a transversedirection to the flow of the cooling air. In this design, the tripstrips 132 are shown as skewed trip strips in that they are angledslightly relative to the direction of the flow of the cooling air. In analternate embodiment, the trip strips 132 can be normal to the flowdirection of the air. Skewed trip strips are sometimes employed overnormal trip strips so as to allow the trip strip to be longer, whichprovides more turbulent airflow.

Because of the temperature and air vortexes experienced by the blades34, the blades 34 need to be periodically inspected. Particularly, it isknown that the trailing edge 82 of the blade 34 is known to exhibiterosion with use over time. Indications in the eroded region aredifficult to detect using the traditional inspection techniques such asliquid penetrant and ultrasonic or eddy current inspection methods. Forexample, during liquid penetrant inspections, the penetrant is used todetect indications as they grow large enough to be detected outside ofthe erosion region. Erosion traps penetrant which bleeds out during thedevelopment process, thereby obscuring relevant indications. Thus, ifthe erosion region extends far enough into the blade, the indicationsmust reach a critical size before they can be regarded as a crack. Inother words, this method give false indications causing blades to bepulled from the turbine when it may not be necessary to do so.Additionally, the surface roughness from the erosion causes inadequatecoupling or large background noise when using ultrasonic or eddy currentinspection methods making relevant indication determinations difficult.

Acoustic thermography can detect small indications that exist only inthe erosion region without suffering the negative effect of the noiserelated to the erosion, as described in the '948 patent issued to Thomaset al. and discussed above. While this method has been applied in thefield with success, it requires the removal of the turbine blades fromthe steam turbine unit. Removal of the blades for inspection is bothcostly and time-consuming, as stated above.

FIG. 4 is an illustration of an embodiment of a system 150 that iscapable of performing in situ acoustic thermography of turbine blades inan assembled steam turbine, where the system 150 is capable of detectingcritical indications in the turbine blades before they extend beyond theerosion region. An air cylinder 152 is used to control a clamping andunclamping function that forces a cap 154 to press against a bladeinserted between the cap 154 and a blade stop 156 as described in moredetail below. The blade stop 156 is attached to an end frame portion172. Opposite to the blade stop 156 on the end frame portion 172 may bea protective bottom plate 174 that protects the blades being inspectedfrom damage from the end frame portion 172. This is necessary becausethe blade that is being inspected is clamped at a trailing edge regionand not at a blade root region as is done according to known methods inthe art. Any suitable material, such as plastic, may be used for theprotective bottom plate 174. The blade stop 156 may be any suitablematerial, including plastic. The cap 154 serves to dampen the signal toprotect a blade that is inserted between the cap 154 and the blade stop156 from being damaged. The cap 154 is preferably made from brass.Copper, or a mixture that includes copper and brass may be used for thecap 154. The cap 154 is on an end portion of an acoustic thermographystack that is opposite to a horn 158 that is typically made of titaniumor a similar material. The cap 154 also serves to protect the horn 158from becoming brittle and sustaining damage from use. The horn 158 isconnected to a piezoelectric portion 160 that is connected to a booster162 that amplifies the energy of the horn 158 such that a blade that isclamped inserted between the cap 154 and the blade stop 156 is excitedusing the energy of the horn 158 in a manner known to those skilled inthe art. The booster 162 may be any suitable material, including carbonsteel. The horn 158, the piezoelectric portion 160, the booster 162 andthe cap 154 make up the acoustic thermography stack.

An aluminum bracket 164 clam-shells around the piezoelectric portion 160and is connected to a block 168 that is slidably moveable along a track166 of a frame 170. Air pressure from the air cylinder 152 moves theclamp 164 that holds the horn 158, piezoelectric portion 160, booster162, and cap 154 (i.e., the stack) up and down the track 166 to clampand unclamp a blade as discussed in detail below. A stack support 176 isattached to the clamp 164 and is used to provide stabilizing support tothe piezoelectric portion 160 of the stack.

FIG. 5 is an illustration of an embodiment of a system 200 forperforming acoustic thermography of turbine blades in an assembled steamturbine, where like elements are identified by the same referencenumerals used in FIG. 4. The system 200 is brought inside the turbinethrough an access door (not shown) so that assembled blades in theturbine may be inspected. An air hose 202 provides air to the system200, and an air hose 204 provides air to the air cylinder 152 uponactuation. Actuation may occur, for example, via an actuating switch212. However, any suitable method and/or mechanism for actuation may beused. A pressure regulator 208 and a pressure gauge 210 may be used toadjust pressure to the air cylinder 152 in a manner known to thoseskilled in the art. The air pressure used may vary to provide a desiredclamping force. For example, the pressure used to clamp a blade may be35 psi.

Using the air cylinder 152 to move the stack up and down as describedabove, a blade 220 is clamped between the cap 154 and the blade stop156. Once the blade 220 is clamped into place, the blade 220 is excitedand inspected as described above. Next, the blade 220 is unclamped andthe system 200 is moved such that a blade 222 may be clamped andinspected. This process is repeated such that blades 224 and 226 areinspected. After the blades that are accessible are inspected, forexample the blades 220-226, the rotor that the blades are mounted to isturned such that a next set of blades may be inspected. This process isrepeated so that all of the blades may be inspected in situ.

FIG. 6 is an illustration of an infrared camera 300 that is being usedwith the system 200 according to one embodiment of the invention. Thecamera 300 is mounted on a tripod 302 such that the camera 300 maycapture a blade that is being excited by the system 200. A plug 304provides electrical power to the system 200, and a cable 306 plugs intoa computer or computing device via, for example, a USB port. In thisway, the system 200 is able to excite a desired blade, and the infraredcamera 300 is able to capture images of the excited blade and providethe images to a computer such that a proper analysis/inspection of theblade may be performed. The computer may be a laptop that is broughtinside the turbine, or the computer may be external and connected via along cable or by using a USB/Ethernet converter in a manner known tothose skilled in the art. The system 200 may also be controlled remotelyusing a computer with the appropriate software, or may be mechanicallyoperated by a technician. One or more indicator stickers 308 are placedon the blades to be inspected and are used as signal indicators toverify excitation of a blade has occurs during analysis to confirm thata blade is excited enough to detect a crack or damage in the blade.Thus, if the blade being inspected is not damaged, the camera 300 willnot indicate anything in the blade. The indicator sticks 308 will be theonly indication that the blade has been excited enough to adequatelyinspect. If the indicator stickers 308 do not light up in the cameraimages, it may be determined that the blade being inspected was notexcited enough to provide adequate inspection.

FIG. 7 is an illustration of the infrared camera 300 being used with thesystem 200 according to another embodiment. In this embodiment, thecamera 300 is mounted to a strap 312 and positioned to capture a bladebeing excited by the system 200. The camera 300 may be adjusted suchthat it is in a desired position along the strap 312. The strap 312 maybe any suitable strap, such as a ratchet strap. The strap 312 extendsall the way around a cylinder 310 of the turbine. Although not shown,brackets or any suitable mechanism may be used to attach the camera 300to the strap 312.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the scope of the invention asdefined in the following claims.

What is claimed is:
 1. A system for performing acoustic thermographyinspection of turbine blades while the turbine blades are in place in anassembled turbine, said system comprising: an acoustic thermographystack that includes a horn, a piezoelectric portion, a booster and acap; a frame that the acoustic thermography stack is slidably mounted tosaid frame including an end frame portion with a blade stop; an aircylinder that provides force to move the acoustic thermography stack upand down a rail of the frame such that a turbine blade may be clampedbetween the cap and the blade stop and then excited using the acousticthermography stack; and an infrared camera, said infrared camera beingused to detect critical indications in the turbine blade that is clampedbetween the cap and the blade stop and then excited, wherein the cap ismade of brass, copper, or a mixture that includes copper and brass. 2.The system according to claim 1 further comprising a clam-shell clampthat clamps the piezoelectric portion of the acoustic thermography stackto a rail of the frame.
 3. The system according to claim 1 furthercomprising a bottom plate of the end frame that protects turbine bladesfrom being damaged.
 4. The system according to claim 1 wherein the bladestop is made of plastic.
 5. The system according to claim 1 wherein theinfrared camera is seated on a tripod.
 6. The system according to claim1 wherein a trailing edge region of the blade is clamped between the capand the blade stop.
 7. The system according to claim 1 furthercomprising one or more indicator stickers placed on each of the bladesto be inspected, said indicator stickers indicating when the turbineblade being inspected has been excited enough to provide a properinspection, wherein the indicator stickers indicate when the turbineblade being inspected has been excited enough to provide a properinspection by lighting up in a camera image.